电机学（第七版）（修订版）课件 Chapter-5-Synchronous-Machines

Chapter5SynchronousMachines7/10/2024SynchronousMachines1IntroductionTheDCfieldisnormallyontherotorandACarmaturewindingisonthestatorDCfieldcurrentsetsupmainair-gapfluxandACarmaturehandlestheelectricalpowerRotorrotatesinsynchronismwiththemagneticfieldsetupbythearmaturewindingsRotorspeedisproportionaltothefrequencyofthearmaturecurrentsinsteadystate7/10/2024SynchronousMachines2Stator-rotormutualinductanceis

Laf

cos(qme)Insteadystate

qme=wet+de0Open-circuitarmaturevoltageis 7/10/2024SynchronousMachines3Simplifiedthree-phasesynchronousmachineStatormutualinductanceis Lab=Laa0cos(120˚)=-½Laa0Statorselfinductanceis La=Laa0+Lal

Balancedthree-phasecurrentsia+ib+ic=0 7/10/2024SynchronousMachines47/10/2024SynchronousMachines5Motorsignconventionsimplymeansthereferencedirectionsarechosenfornormalmotoroperation7/10/2024SynchronousMachines6Synchronous-machineequivalentcircuits:(a)motorreferencedirectionand(b)generatorreferencedirection.7/10/2024SynchronousMachines7IaVa(Ra+jXs)IaEafIaEaf(Ra+jXs)IaVaSynchronousmotorandgeneratorphasordiagramsbothhavinglaggingpowerfactorattheterminals(IalaggingVa)MotorGenerator5.3Open-andShort-CircuitCharacteristicsTheopen-circuitarmaturevoltageandshort-circuitarmaturecurrent,bothplottedversusthefieldcurrent,allowcomputationofthesynchronousreactanceXsOpen-circuitcharacteristicwillshowsignificantsaturationandisoftencalledopen-circuitsaturationcurveShort-circuitcharacteristic(plotteduptoslightlyaboveratedcurrent)willnot,sincetheexcitationislowtheseconditions7/10/2024SynchronousMachines87/10/2024SynchronousMachines9Open-andshort-circuitcharacteristicsshowingequivalentmagnetizationlineforsaturatedoperatingconditions7/10/2024SynchronousMachines10SaturatedandunsaturatedvaluesofXs:SaturatedandunsaturatedvaluesofXsinperunit:Inlargesynchronousmachines,thearmatureresistanceismuchsmallerthanthesynchronousreactance.5.4Steady-StatePower-AngleCharacteristic7/10/2024SynchronousMachines11(a)Impedanceinterconnectingtwovoltages(b)phasordiagramMaximumpowerdeliveredbyasynchronousmachineisaspecialcaseofpower-anglecharacteristicforpowertransferthroughaseriesimpedanceZ=R+jX,fromE1toE2ForsimplicityZjX7/10/2024SynchronousMachines125.5Steady-StateOperatingCharacteristics7/10/2024SynchronousMachines13Constructionusedforderivationofasynchronousgeneratorcapabilitycurve.7/10/2024SynchronousMachines14ThisequationgivesthefieldheatinglimitThearmatureheatinglimitissimplythemachinevolt-ampererating(ratedcurrentatratedterminalvoltage)7/10/2024SynchronousMachines15Phasordiagramforconstant-poweroperationatconstantterminalvoltage.NotethatlesslaggingormoreleadingcorrespondstosmallerexcitationvoltagemagnitudeEafandsmallerfieldcurrentIfIa3VajXsIa2Eaf1Ia2Ia1Eaf3Eaf2jXsIa3jXsIa17/10/2024SynchronousMachines16SynchronousGeneratorVCurves5.6EffectsofSalientPolesIntroductiontosynchronouslyrotatingdqaxistheoryResolvearmaturephasorsintodandqaxiscomponentsDirect(d)axisisalignedwithfieldpoles,quadrature(q)axisismidwaybetweenpoles7/10/2024SynchronousMachines177/10/2024SynchronousMachines18Inductanceisfluxlinkageperunitampere:Thed-axiscurrentproducesMMFthatseesashortairgap(acrosspolefaces)sothed-axisinductanceislargeTheq-axiscurrentproducesMMFthatseesalongairgap(interpolarregion)sotheq-axisinductanceisrelativelysmallSalient-polemachinesareanalyzedwithaphasordiagramrepresentingd-andq-axisquantitiesseparately:IdseesXdandIqseesXqwhereXd>XqNosimpleequivalentcircuitisavailable7/10/2024SynchronousMachines197/10/2024SynchronousMachines20Phasordiagramforasalient-polesynchronousgenerator.7/10/2024SynchronousMachines21Phasordiagramillustratingthetechniqueforlocatingthequadratureaxisgivenarmatureterminalvoltage,currentandpowerfactorPermanent-MagnetACMachinesPolyphasesynchronousmachineswithpermanent-magnetrotorsareuseful,withmanyapplicationsparticularlyasmotorsTheanalysisissimilartothatalreadydiscussed,excepttheexcitationisnotadjustablePermanent-magnetmotorsareusuallyoperatedfromvariable-frequencymotordrives7/10/2024SynchronousMachines227/10/2024SynchronousMachines23Schematicdiagramofthree-phasepermanent-magnetacmachine.Thearrowindicatesthedirectionofrotormagnetization.Thismachinecanbeanalyzedasifitwereawound-fieldmachinewithconstantfieldcurrent.Thecontrolofapermanent-magnetacmotoroftenusesarotorpositionsensor.SummaryThesynchronousmachineisanalyzedundersteady-stateoperatingconditionsPolyphasecurrentsonthestato